The present invention relates to a rotary head device and a magnetic head unit having plural magnetic heads on a rotary member and a head base, used in magnetic recording and reproducing apparatus such as VTR, and a manufacturing method thereof.
FIG. 9 is a structural diagram of a magnetic head unit used in a conventional rotary head device for VHS system. Magnetic heads 31, 32 are fixed on a head base 33. In a manufacturing process of magnetic heads, usually, the front surfaces of the magnetic heads 31, 32 are finished along the sliding direction S and the thickness direction T (vertical direction to the sheet of paper) orthogonal to the sliding direction S to specified dimensions by tape polishing process, after machining. More specifically, first, the front surfaces Ss of the magnetic heads 31, 32 are machined by leaving an allowance for finishing by tape polishing process. Then, by using a polishing tape, the front surfaces Ss are processed in curvature to the portion indicated by broken line R in FIG. 9, after being adhered to the head base 33.
As shown in FIG. 9, when the magnetic heads 31, 32 are processed simultaneously, the front surfaces Ss are processed along the sliding direction S over two magnetic heads 31, 32. In the conventional magnetic head for VHS system, the gap M of the two magnetic heads 31, 32 is about 0.7 mm. The thickness of the magnetic recording tape for VHS system is about 20 microns. Therefore, even in the magnetic heads finished over two magnetic heads, the magnetic heads contact with the magnetic tape smoothly.
In the recent digital VTR, in order to cope with various functions, the gap M of the magnetic heads is extended to 1.2 to 4.5 mm. The thickness of the magnetic tape for the digital VTR to realize high recording density is very thin, as compared with the magnetic tape for VHS system, and is nearly 7 to 14 microns. In the rotary head device in such digital VTR, therefore, the magnetic tape may sink in between the magnetic heads and may be damaged by the edges of the magnetic heads. To prevent this damage, it is necessary to finish individually the curved surfaces Ss along the sliding direction S of the individual magnetic heads.
FIG. 10 is a plan view of a conventional magnetic head unit for a digital VTR after processing. Radii Rs.sub.1, Rs.sub.2 of curved surfaces Ss along the sliding direction S of the magnetic heads 31, 32 fixed on the head base 33 are identical. However, the positions of their centers Or.sub.1, Or.sub.2 are different.
In a conventional method of manufacturing the magnetic head unit for the digital VTR, the process is complicated, that is, once the respective magnetic head is fixed on a provisional base, and the curved surface is processed by tape polishing. Then, the respective magnetic head is dismounted from the provisional base, and the plural magnetic heads 31, 32 are fixed on the head base 33 as the final step.
In the conventional magnetic head unit, since the radii Rs.sub.1, Rs.sub.2 of adjacent magnetic heads 31, 32 are identical, optimum conditions are not obtained for improving the contact state between the head and tape due to effects of the layout of plural magnetic heads 31, 32 on the common head base 33, and for reducing the wear of heads.
Moreover, when disposing multiple magnetic heads on a smaller rotary drum for high density recording, the ratio of area occupied by the magnetic heads including head base on the rotary drum is high. Therefore, the design is much limited in the fixing method of rotary drum on the rotor, and connecting method of magnetic heads and rotary transformer unit. Still more, to cope with higher recording data rate, if the number of magnetic heads is increased, the space for disposing the head base is limited, and it is more difficult to realize.